1. Field of the Invention
The present invention relates to a surface inspection apparatus for inspecting a surface of a photomask or the like, and particularly relates to the surface inspection apparatus for inspecting whether or not there is a particle of dust and/or a flaw on the surface of the photomask or the like.
2. Description of the Related Arts
Generally, if there is a particle of dust or a flaw on a mask surface of a photomask which is used for exposing a semiconductor wafer to a light so as to correspond to a circuit pattern, the particle of dust or the flaw is exposed to the light as a part of the circuit pattern. As a result, a wafer with a defect is produced. Accordingly, it is crucially important to prevent the particle of dust or the flaw from being deposited or formed on the photomask.
In order to prevent the dust or flaw from being on the photomask, a visual final inspection thereof has been performed conventionally. The visual final inspection thereof is carried out after an inspection with an automatic inspection apparatus is done, as a conventional common practice. The reason why the visual final inspection is carried out is that the automatic inspection apparatus has a stationary camera which is used for scanning the mask surface only level or in a direction generally perpendicular to the surface thereof. That is, the mask surface thereof can not be inspected in different directions with the stationary camera; therefore, there is a possibility that the stationary camera may overlook the particle of dust or the flaw thereon. This visual final inspection has been conventionally carried out completely manually.
More specifically, at the step of the visual final inspection, an inspector inspects the photomask in such a manner that he/she visually observes the mask surface under a lighting while he/she is changing the angle between the mask surface and the lighting, while manually holding the photomasks one by one. At this step thereof, if there is a particle of dust or a flaw on the mask surface, the defect can be found by observing any specific, irregular reflection caused thereby.
The method is, however, extremely primitive. According to the method, because the inspector directly holds the photomask with his/her own hand, the photomask may be, on the contrary, spoiled by a particle of dust adhered on the mask surface thereof with the inspector's intervention.
Further, when the inspector repeats the inspecting process many times, the inspector's hand is fatigued, and the efficiency of the inspection thereof is significantly lower.
Furthermore, in addition to the visual inspection on the mask surface, it is necessary to do such extra works as fixing the position of the photomask, or inclining the photomask ideally, which also cause an inefficiency in the inspecting work.
In order to solve these problems, it is conceivable that the photomask is handled with a robot, or the like, in a space which is isolated from the inspector, where the photomask is placed onto an inspection stage and the inspector visually inspects the photomask through an observation window. In such system, it is desirable to do a remote control or do an automatic control of the photomask so that the photomask is carried from place to place in the system and is properly handled, and so that the photomask which is placed on the inspection stage is positioned relative to the inspection stage, is moved, and is inclined.
Meanwhile, as to the inspection of the wafer, there has been conventionally provided a surface inspection apparatus which allows the inspector to visually inspect the wafer without directly touching it. This surface inspection apparatus is equipped with a suction disk for sucking the wafer which is placed on top of the suction disk, in which the suction disk is inclinable generally in a circular arc about pivot located in lower part of the apparatus. The inspector, while inclining the wafer by operating a joy stick, performs a visual inspection under an illumination of a spotlight, or a lighting.
However, according to this surface inspection apparatus, when the wafer is intentionally inclined for a review of observation, detailed investigation, and/or checking of a defect of the wafer from a different angle, upon a discovery of the defect thereof, the defect moves together with the wafer due to the inclination of the wafer. Accordingly, with the surface inspection apparatus, there arises a problem that the inspector is prone to lose sight of the defect of the wafer.
Particularly, when the spotlight is made to be smaller at the time of the inspector's trying to do a more precise inspection of the wafer, only a small part of the wafer surface is illuminated or lit by the spotlight with the inspection range being narrower. At this time, the defect of the wafer immediately goes out of the inspection range if the inspector tilts or inclines the wafer.
Meanwhile, it is desirable that this type of surface inspection apparatus is as compact as possible.